DE102017104064B4 - Process for operating a continuous furnace and continuous furnace - Google Patents

Abstract

Method for operating a continuous furnace (24) for heating a material lying on an endlessly circulating conveyor belt (2) by means of microwaves, comprising: a treatment space (4) and at least one absorption area (16) arranged before and/or after the treatment space (4), wherein radiation (5) is generated by means of microwave generators and is introduced into the treatment room (4) by means of waveguides via openings (6) in the wall of the treatment room (4) and/or the radiation (5) is generated directly in the treatment room (4) by means of microwave generators , wherein a residual radiation (13) in the absorption area (16) is absorbed by at least one absorption element (18), characterized in that the power input of microwave power into the treatment chamber (4) depends on the residual radiation (13 ) is controlled or regulated.

Description

The invention relates to a method for operating a continuous furnace for heating a material by means of microwaves according to claim 1 and a continuous furnace for heating material by means of microwaves according to claim 6.

In the production of material panels, in particular wood-based panels made of lignocellulose-containing material, it is known to preheat the material scattered to form a fleece before pressing it in a press. Due to the higher heat at the beginning of the pressing, the press needs less time to heat the fleece completely. Accordingly, the press can be designed to be shorter or operated faster. Hot air or steam preheating systems or the use of high-frequency radiation, for example microwaves, for preheating in microwave continuous ovens, referred to below as continuous ovens, have proven particularly effective. The physical principle is based on the conversion of electromagnetic energy into thermal energy when the microwaves are absorbed by the material to be heated.

For example, that's how it is DE 197 18 772 A1 or DE 10 2015 107 374 A1 It is known to expose the material scattered to form a fleece to microwaves before introducing it into a heated, preferably continuously operating press, in order in this way to accelerate a subsequent heating and pressing process. Heating with microwaves has the advantage that the desired heat is generated directly in the product by the microwaves penetrating the product, being absorbed and stimulating existing water molecules or other electrical dipoles to oscillate. In contrast to this, when using heating plates or hot-air preheating systems or the like, the heat is essentially applied from the outside, which means that complete penetration of the product to be manufactured with this heat cannot always be guaranteed. In the case of products preheated by means of microwaves, such a heat distribution can be observed in the heated press that the core of a product also reaches a desired temperature without critical temperatures already being exceeded during pressing in the areas further out.

Compared to the use of steam preheating systems, the use of microwaves has the advantage that no additional moisture is introduced into the material to be pressed during preheating. Due to the additional moisture that is introduced with the steam preheating systems, the material must be dried before it is applied to the conveyor belt in such a way that the maximum moisture content of the material is not exceeded before pressing by adding moisture, for example steam. This leads to intensive drying of the material and high energy consumption even during the pre-treatment of the material.

When using microwaves or high-frequency radiation in a continuous furnace to heat the material, intensive drying of the material under maximum moisture in advance can be dispensed with, which has a positive effect on the energy balance. But the continuous furnace also has a certain output, which can range from a few kW to a few hundred MW or more, depending on the material and area of application. The service entry is determined for one or more materials and the corresponding recipe is stored. However, the material can also be subject to certain material fluctuations, so that the optimal temperature of the material cannot always be reached after exiting the continuous furnace, or a large part of the microwave radiation is destroyed in the absorption range.

The object of the present invention is therefore to specify a method for operating a continuous furnace and a continuous furnace with which the energy efficiency of the continuous furnace can be optimized, adjusted and adjusted.

The object of the method is achieved according to the invention in that the power input of microwave power into the treatment room is controlled or regulated as a function of the residual radiation measured in the absorption area.

The object of the device is also achieved by a continuous furnace for heating material by means of microwaves, comprising one or more microwave generators for generating radiation; a treatment room for heating the material, with one or more openings for introducing the radiation into the treatment room via waveguides being arranged in the treatment room and/or the microwave generators being arranged directly in the treatment room, an endlessly circulating conveyor belt for transporting the material through the continuous furnace; and at least one absorption area, which is arranged before and/or after the treatment room, with at least one absorption element for absorbing residual radiation being arranged in the absorption area, with a measuring device for determining the residual radiation being arranged in the absorption area, which is equipped with a control device for controlling or regulating the Power input interacts with microwave power in the treatment room.

With a method according to the invention and the device according to the invention, the energy supply into the material can then be controlled or regulated via the microwave generator directly or via the waveguides via a control device with the resulting measured values in such a way that the residual radiation in the absorber is reduced to a minimum.

In principle, the residual radiation can be measured and recorded at several points along the production direction and transverse to the production direction in order to be able to control or regulate the energy distribution within the continuous furnace with these measured values in addition to monitoring the temperature and to be able to improve the absorption behavior of the material accordingly .

The absorption elements are preferably designed as absorption plates, which are arranged in a regular or irregular pattern in the absorption chamber. All materials that can absorb microwave radiation and convert it into heat are suitable as absorption elements. For example, a water tank can also be arranged as an absorption element.

In a preferred embodiment, the power loss in the absorption area is measured to determine the residual radiation. The amount of power generated by the residual radiation in the absorption area is referred to as power loss. The power loss thus indicates the amount of power that was not absorbed by the material itself. By measuring the residual radiation in the absorption range, it can be determined how much power was not or could not be absorbed by the material. The control device can make it possible to reduce the power loss if, for example, the temperature of the material still corresponds to the desired material temperature after passing through the continuous furnace.

Alternatively or in combination, the temperature of the at least one absorption element can be measured to determine the power loss. The absorption elements absorb the residual radiation in the absorption area, which is then converted to heat in the absorption elements and leads to heating of the latter. The residual radiation in the absorption area is preferably distributed in such a way that the absorption elements heat up evenly.

In an alternative embodiment it can be provided that the power input is controlled and/or regulated via the power of the microwave generator and/or via power regulators in the waveguide. The power input can be controlled or regulated by changing the power of the microwave generators, so that less power input is provided by the microwave generators. Alternatively or in combination, when waveguides are used, power regulators can be introduced into them, which minimize the power generated by the microwave generators in the waveguide, so that less microwave power is introduced into the treatment room.

The material is preferably designed as a mat or fleece.

In a further preferred embodiment of the continuous furnace, the measuring device is designed as a temperature sensor in the absorption area for determining the temperature of the at least one absorption element.

An alternative embodiment is characterized in that power regulators are arranged in the waveguide to control or regulate the power input and/or the power of the microwave generator can be controlled or regulated.

The speed of the conveyor belt can preferably be controlled or regulated as a function of the temperature of the material downstream of the continuous furnace. By choosing the right speed at which the material is transported through the continuous furnace, the absorption of the material can also be influenced.

Further advantages and features of the invention result from the following description of an exemplary embodiment.

• 1 eine Prinzipskizze eines Durchlaufofens;
• 2 eine weitere Prinzipskizze eines Durchlaufofens;
• 3 eine dritte Prinzipskizze eines Durchlaufofens;
• 4 einen Teil-Ausschnitt der 3 mit dem Absorptionsbereich
• 5 eine Aufsicht auf den Teil-Ausschnitt aus 4;
• 6 eine detaillierte Ansicht einer Absorptionskammer.

It shows:

• 1 a schematic diagram of a continuous furnace;
• 2 another basic sketch of a continuous furnace;
• 3 a third basic sketch of a continuous furnace;
• 4 a partial excerpt of the 3 with the absorption range
• 5 a top view of the partial section 4 ;
• 6 a detailed view of an absorption chamber.

In 1 shows a section through a continuous furnace 24 for heating a material, which in the present case is in the form of a fleece or mat 1, by means of high frequency radiation or microwave energy in side view. In this continuous furnace 24, a mat 1 of lignocellulosic material mixed with a binder, which is usually endlessly scattered in a spreading station, is continuously guided through a treatment chamber 4 by means of two conveyor belts 2, 3 running endlessly around deflection rollers, in which the mat 1 is exposed to radiation 5, in particular microwave radiation, is irradiated from below and/or above. The two conveyor belts 2, 3 are made of a material that is transparent to the radiation 5 and run parallel to one another, with the lower conveyor belt 2 carrying the mat 1 and the upper conveyor belt 3 covering the mat 1 at the top. The use of an upper conveyor belt 3 is optional but offers some advantages. The upper conveyor belt 3, which rests on the mat 1, on the one hand has the function of protecting the surface of the mat 1 when it runs through the continuous oven 24 and on the other hand it also prevents material, for example product fibres, dust, etc. , Easily released from the mat 1, fly around and then in the continuous furnace 24, in particular in the treatment room 4, can be reflected or deposited in some places and can thus lead to operational disruptions.

In the treatment room 4, the radiation 5 is preferably introduced above and below the mat 1 in order to ensure that the mat 1 is heated evenly. The radiation 5 can be generated by means of microwave generators (not shown) outside of the continuous furnace 24 and can be coupled into the treatment space 4 of the continuous furnace 24 by means of waveguides via openings 6 . Alternatively, the radiation 5 can also be generated within the treatment room 4, which means that waveguides and the corresponding openings 6 can be dispensed with. The radiation generators for radiation generation within the treatment room 4 or the openings 6 for the entry of the radiation 5 into the treatment room 4 are preferably arranged at a distance from the mat 1 in order to enable spatial propagation of the radiation 5 in the entire treatment room 4 . The treatment room 4 therefore has a clear height 10 which indicates the vertical distance between the openings 6 and the microwave generator above and below the mat 1 . The clear height 10 of the treatment room 4 can also be seen as the distance between the surfaces of the treatment room 4, which are aligned parallel to the surface side of the mat 1.

In the area of the treatment room 4, the lower conveyor belt 2 runs with its underside over a plate 7 that is permeable to the radiation 5 or microwaves. Instead of a plate 7 made of material permeable to microwaves, a lattice construction or similar can be provided, which allows the radiation 5 to pass through and at the same time can take on a carrying function, so that the lower conveyor belt 2, which is loaded with the weight of the mat 1, does not sag .

The radiation 5 effects a continuous preheating in the mat 1 essentially over the residence time in the continuous furnace 24 . After leaving the continuous furnace 24, the mat 1 preheated in this way is pressed and cured in a press (not shown) to form a material board, in particular chipboard, MDF or OSB board.

In this press, the mat 1 is subjected to pressure and heat, so that the binder present in the mat 1 is fully activated, hardens and connects the materials or particles present in the mat. Due to the preheating already effected in the continuous furnace 24, the temperature required for the activation of the binder is reached more quickly in the press. This has a positive effect on the production process in many ways. For example, the mat 1 can be run through the press at a higher speed, since the higher temperature of the mat 1 when it enters the press can reduce the time it remains in the press until the mat has completely hardened. This can lead to a further increase in production. At the same time, due to the preheating, the heat applied from the outside for further heating within the press can no longer generate a temperature gradient within the mat 1, in which the temperature in the outer area of the mat 1 already reaches a value that is harmful to the binding agent or the surface, while in the innermost core of the mat 1, a minimum temperature necessary for the activation of the binder has not yet been reached.

So that the radiation 5 from the treatment room 4, in which it was introduced into the mat 1, are not emitted in an undesired manner, locks 9 are provided in the production direction 8 before and/or behind the continuous furnace 24, through which microwaves can escape from the Continuous furnace 24 is to be prevented from entering the environment. The position of the sluice 9 can be adapted for each mat height 15 and width of the mat 1 in such a way that only a minimal gap is created between the sluice 9 and the mat 1, which the radiation 5 cannot pass through. The radiation 5 is thus reflected back at the lock in the direction of the treatment room.

To increase the absorption rate of radiation 5, a channel 11 is arranged directly adjacent in the production direction 8 before and/or after the treatment room 4, the wall 12 of which is microwave-tight and thus that in the channel 11, for example residual radiation 13 that has entered from the treatment room 4 is reflected. Residual radiation 13 entering this channel 11 is, insofar as it is not absorbed in the mat 1 running through this channel 11, reflected on the wall 12 and introduced again into the mat 1, where it is then at least partially absorbed with thermal heating of the mat 1 .

This occurs both in the direction of production 8 in the channel 11 downstream of the treatment room 4 and counter to the direction of production 8 in the channel 11 upstream of the treatment room 4.

The clear height 14 of the channel 11 can be adapted to the mat height 15 so that the reflected residual radiation 13 is reflected immediately into the mat 1 and the possibility of further absorption of the residual radiation 13 by the mat 1 exists. As a result, the residual radiation 13 present in the channel 11 is predominantly conducted through the mat 1, as a result of which the absorption rate is significantly increased. For this purpose, the wall 12 of the channel 11 arranged above the mat 1 can be lowered independently of the treatment room, so that it lies flat on the surface of the mat 1 or on the upper conveyor belt 3 covering it at the top. Depending on the materials used, the wall 12 and conveyor belt 3, it can also make sense to form a minimum distance of less than 5 cm, preferably less than 3 cm, particularly preferably less than 1.5 cm, in order to avoid friction between the wall 12 and the conveyor belt 3, for example.

Alternatively or in combination, it is also conceivable to form the wall 12, in particular the wall 12 above the mat 1, with elements for reflection, which reflect the residual radiation 13 present in the channel 11 in such a way that it is scattered or reflected in the direction of the treatment room 4.

If necessary, the microwave-reflecting wall 12 of the channel 11 can be adjusted telescopically in its active length, which is not shown in detail in the present drawing. A change in the length of the channel 11 offers the advantage that the residual radiation 13 present in the channel 11 can be reflected over a longer distance and the residual radiation 13 is thus absorbed more intensely in the mat 1 . The length of the channel 11 is preferably adjusted in such a way that a lock 9 is no longer necessary at the end of the channel 11 and all the residual radiation 13 in the mat 1 has been absorbed.

In 2 Another embodiment of a continuous furnace 24 is shown, which in addition to the already in 1 described elements has an absorption region 16, which is arranged directly adjacent to the channel 11 or in which the channel 11 widens.

As already in 1 Radiation 5 , in particular microwave radiation, is introduced into a treatment room 4 with a clear height 10 . The radiation 5 can be generated directly in the treatment room 4 or radiation 5 generated outside of the continuous furnace 24 can be introduced into the treatment room 4 via waveguides and openings 6 . The entry of radiation 5 can only take place on one side of the treatment room 4 or also from two or all sides of the treatment room 4 . The radiation 5 should be introduced or the radiation 5 generated at a certain distance from the mat 1 so that the radiation 5 can spread in the treatment room 4 . When radiation 5 is introduced below the mat 1 to be heated, which is transported through the continuous furnace 24 via conveyor belts 2, 3, a radiation-transparent, in particular microwave-transparent plate 7 is provided above the openings 6 and below the lower conveyor belt 2 to prevent the mat 1 from sagging arranged. Instead of a plate 7, a grid structure or the like, which is transparent to the radiation 5, can also be arranged.

A channel 11 with a wall 12 extends directly adjoining the treatment room 4 and reflects the residual radiation 13 exiting the treatment room 4 both in and against the production direction 8 and entering the channel 11 . As a result of the reflection, the residual radiation 13 present in the channel 11 is reflected back in the direction of the mat 1 in order to be at least partially absorbed there, as a result of which the absorption rate or absorption of radiation power by the mat 1 increases overall. Both the length and the clear height 14 of the channel 11 can be changed and adjusted to the mat height 15, so that the residual radiation 13 that is present is immediately reflected back into the mat 1 for increased absorption.

In order to prevent radiation 5 from exiting the continuous furnace 24, an absorption region 16 is formed adjacent to the channel 11, in which the residual radiation 13 exiting from the channel 11 and not absorbed by the mat 1 can be converted into heat.

The absorption area 16 comprises an absorption chamber 17 in which absorption elements 18, which are preferably designed as absorption plates, are arranged for absorbing the residual radiation 13. By absorbing the residual radiation 13, the absorption elements heat up mente 18, this heat being given off again by convection or thermal radiation or can be dissipated by ventilation or cooling.

The absorption chamber 17 can be arranged on one side or on both sides of a surface side of the mat 1 . In an arrangement below the mat 1, the opening to the absorption chamber should be covered with a radiation-transparent plate to prevent the mat 1 from sagging, comparable to the plate 7 in the treatment room 4. Such a plate 7 can optionally also be used for one above the mat 1 arranged absorption chamber 17 are used. Particles originating from the mat 1 and other particles therefore do not get into the absorption chamber 17, where they could accumulate and lead to malfunctions, for example by igniting.

Furthermore, the absorption chamber 17 can be constructed from a plurality of segments 21, with the number of absorption elements 18 being able to vary from segment 21 to segment 21. The individual segments 21 can be separated from one another by a partition wall 19 which is aligned perpendicular to the direction of production 8 and runs essentially transversely to the direction of production 8 in the longitudinal direction. The dividing walls 19 have openings 20 so that within a segment 21 residual radiation 13 is partially reflected at the dividing wall 19, but can also partially penetrate into a further segment 21 in order to be converted into heat at the absorption elements 18 there. The openings 20 of two adjacent partitions 19 should have a slight overlap, preferably no overlap, in or counter to the direction of production 8, so that if residual radiation 13 enters a segment 21 through an opening 20, there is a high probability that it will also be reflected in this segment 21 becomes. The absorption elements 18 are preferably arranged parallel to one another in a segment. In particular when using absorption panels as absorption elements 18, these should be aligned in such a way that the surface sides of the absorption panels are arranged perpendicular to the production level in which the conveyor belt 2, 3 also runs. This allows the residual radiation 13 in the absorption chamber 17 to also spread out in the vertical direction. It is therefore also possible for absorption elements 18 to be arranged one above the other in several layers, in order to enable absorption of the residual radiation 13 in the vertical direction as well. The absorption elements 18 in the individual layers can in turn be offset from one another.

Alternatively, the individual segments 21 can be arranged not only horizontally, but also vertically one above the other.

One or more measuring devices 23 can be arranged within the absorption region 16, in particular within the absorption chamber 17, which are used to determine the residual radiation 13 or the power loss or heat generated by the residual radiation 13 at the absorption elements 18. Another measuring device 22 can be arranged directly after the mat 1 exits the continuous furnace 24 to determine the temperature of the mat 1 after it has been heated by the radiation 5. A control device 25 can use the measured values of the measuring devices 22 and/or 23 to determine the Microwave power input into the treatment room 4 can be controlled or regulated by comparing the measured values with predetermined target values and changing the power input accordingly.

The power input of microwave power can be controlled or regulated in various ways. On the one hand, it is possible to use the control device 25 to change the output of the individual radiation generators and adjust them in such a way that a desired setpoint value is achieved at the measuring devices 22 and/or 23 . There is also the possibility of reducing the radiation input into the treatment room 4 by completely switching off the radiation input of radiation 5 via individual openings 6 . Alternatively, there is the possibility of controlling or regulating the power input via power controllers within the waveguide. Power controllers are, for example, certain stops that can be introduced into the waveguide to reduce power.

3 shows another embodiment of a continuous furnace 24, which is similar to 2 is formed with a treatment chamber 4, an adjoining channel 11 and an absorption area 16, with the channel 11 and absorption area 16 being arranged on both sides of the treatment room 4. In the present case, an absorption chamber 17 extends above the mat 1 for absorbing residual radiation 13 . The reflecting wall 12 of the channel 11 is continued below the mat 1 in the absorption region 16 so that the residual radiation 13 is reflected in the direction of the mat 1 and the absorption chamber 17 .

The absorption chamber 17 comprises a plurality of segments 21 in which absorption elements 18 are arranged for the absorption of residual radiation 13, individual segments 21 of the absorption chamber 17 being above in the example shown here of the channel 11 are arranged. A residual radiation 13 of microwaves entering these segments 21 arranged above the channel 11 can thus only enter the absorption chamber 17 through the opening to the absorption area 16 and the segments 21 of the absorption chamber 17 arranged directly in the absorption area 16 . The presence of these segments 21 improves the absorption possibilities in the absorption chamber 17, the arrangement of a part of the segments 21 of the absorption chamber 17 above the microwave-tight wall 12 of the channel 11 being a space-saving solution.
The opening in the absorption area 16 to the absorption chamber 17 can be changed by changing the length of the channel 11, and the absorption of the mat 1 and the residual radiation 13 entering the absorption chamber 17 can thus be influenced. Furthermore, further segments 21 can also be arranged vertically one above the other if this is necessary for the absorption of the residual radiation 13 or if the space requirement in the horizontal direction or in the direction of production 8 is limited.

To adjust the clear height 14 of the channel 11, the absorption chamber 17 is designed to be height-adjustable in the example shown here and can thus be adapted to the mat height 15, as indicated by the arrow in FIG 3 is indicated.

In 4 12 is a detailed section of an area adjoining the treatment room 4, comprising a channel 11 and the absorption area 16 3 shown in more detail. The radiation 5 introduced into the treatment space 4 of the continuous furnace 24 is partially reflected within the treatment space 4 and absorbed by the mat 1 . Part of the radiation 5 can be scattered out of the treatment room 4 and is further reflected in the channel 11 adjoining the treatment room 4 and further parts are absorbed by the mat 1 . Downstream of the channel 11, the residual radiation 13 that is still present in the absorption region 16 can enter the absorption chamber 17, where it passes through the partitions 19 and the chamber wall into the various segments 21 of the absorption chamber 17, in particular into the segments 21 which are arranged above the channel 11 , Scattered or reflected and can be converted into heat at the absorption elements 18 . One or more measuring devices 23 can be arranged on the absorption elements 18 and/or in the absorption chamber 17 itself in order to determine the residual radiation 13 or the heat generated by the residual radiation 13 on the absorption elements 18 . The clear height 14 of the channel 11 as well as the distance between the absorption chamber 17 and the mat 1 can be adjusted to the individual mat height 15 independently of the height 10 of the treatment room 4 . Optionally, a lock 9 can be arranged at the outer end of the absorption area 16 remote from the treatment chamber 4 in order to completely shield the continuous furnace 24 from the environment.

5 shows a plan view of the in 4 shown section through part of a continuous furnace 24. The absorption elements 18 are arranged differently in the segments 21 for optimal absorption of the residual radiation 13 entering the absorption chamber 17. The density of absorption elements 18 should be highest on the segment 21, which is furthest from the Treatment room 4 is removed and borders on the environment to ensure that the residual radiation 13 located there is converted into heat in the absorption elements 18 and cannot escape from the absorption chamber 17 and the continuous furnace 24 . Optionally, a lock 9 can be arranged for further shielding of the continuous furnace 24, which can be set to a minimal gap to the mat 1, so that no residual radiation 13 can escape from the absorption area 16 or the continuous furnace 24 and is reflected back again. In the further segments 21 the density of absorption elements 18 per segment 21 can decrease in order to partially allow the residual radiation 13 to spread there in the absorption chamber 17 and to scatter the residual radiation 13 into the further segments 21 . The arrangement of the absorption elements 18 from segment 21 to segment 21 can preferably be offset from one another. The absorption elements 18 should preferably not be fitted in front of an opening 20 in the partition wall 19 in order to allow the residual radiation 13 to propagate from one segment 21 to the other.

In these partitions 19, as in the 6 as can be seen, a plurality of openings 20 are provided. The residual radiation 13 , in particular microwaves, can pass through these openings 20 into a further segment 21 of the absorption chamber 17 and be directed onto the absorption elements 18 . In this way, the absorption already described by the absorption elements 18 is distributed as evenly as possible and causes approximately the same temperatures everywhere, so that any measuring devices 23 determine a measured value that is similar within the scope of the measuring accuracy.

The absorption elements 18 are arranged essentially perpendicular and normal to the partition wall 19, so that they are parallel to one another. In adjacent segments 21 of the absorption chamber 17, which are separated from one another by the partitions 19, the absorption elements 18 can be both with different Distances as well as offset from each other, the latter bringing thermal benefits. In particular, the residual radiation 13 entering the segments 21 can be distributed uniformly to a large number of absorption elements 18 by reflection on the walls of the absorption chamber 17 and on the partition walls 19, as a result of which these heat up evenly without producing undesirable hot spots. Alternatively or in combination, the absorption elements 18 can be arranged at a certain angle to the partition wall 19 and to the production direction 8 in order to achieve increased absorption.

reference list

1

mat

2

conveyor belt

3

conveyor belt

4

treatment room

5

radiation

6

opening

7

plate

8th

production direction

9

sluice

10

Height

11

channel

12

wall

13

residual radiation

14

clear height

15

mat height

16

absorption area

17

absorption chamber

18

absorption element

19

partition wall

20

opening

21

segment

22

measuring device

23

measuring device

24

continuous furnace

25

control device

Claims (8)

Method for operating a continuous furnace (24) for heating a material lying on an endlessly circulating conveyor belt (2) by means of microwaves, comprising: a treatment space (4) and at least one absorption area (16) arranged before and/or after the treatment space (4), wherein radiation (5) is generated by means of microwave generators and is introduced into the treatment room (4) by means of waveguides via openings (6) in the wall of the treatment room (4) and/or the radiation (5) is generated directly in the treatment room (4) by means of microwave generators , wherein residual radiation (13) in the absorption area (16) is absorbed by at least one absorption element (18), characterized in that the power input of microwave power into the treatment chamber (4) depends on the residual radiation (13 ) is controlled or regulated. procedure after claim 1 , characterized in that to determine the residual radiation (13), the power loss in the absorption area (16) is measured. procedure after claim 2 , characterized in that the temperature of the at least one absorption element (18) is measured to determine the power loss. Method according to one of the preceding claims, characterized in that the power input is controlled or regulated via the power of the microwave generator and/or via power controllers in the waveguide. Method according to one of the preceding claims, characterized in that a mat (1) or a fleece is heated in the continuous furnace (24) as the material. Continuous furnace (24) for heating material by means of microwaves, comprising one or more microwave generators for generating radiation (5); a treatment room (4) for heating the material, one or more openings (6) for introducing the radiation (5) into the treatment room (4) via waveguides being arranged in the treatment room (4) and/or the microwave generators in the treatment room (4) are arranged directly; an endlessly circulating conveyor belt (2) for transporting the material through the continuous furnace (24); and at least one absorption area (16) which is arranged before and/or after the treatment room (4), at least one absorption element (18) for absorbing residual radiation (13) being arranged in the absorption area (16), characterized in that a measuring device (23) for determining the residual radiation (13) in the absorption region (16) is arranged, which with a control device (25) for controlling or Regulation of the power input to microwave power in the treatment room (4) interacts. continuous furnace after claim 6 , characterized in that the measuring device (23) is designed as a temperature sensor in the absorption area (16) for determining the temperature of the at least one absorption element (18). Continuous furnace according to one of Claims 6 or 7 , characterized in that power regulators are arranged in the waveguide to control or regulate the power input and/or the power of the microwave generator can be controlled or regulated.

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